Various methods and apparatuses have been proposed and, by using these methods and apparatuses, various liquid materials including: a liquid adhesive for adhering a pair of optical disc substrates; a liquid resin for forming a resin layer which protects a surface of a disc substrate; a photoresist material or a soldering paste used during a production step of electric parts; and the like, are supplied to an object member. For example, there have been demands with regard to optical discs, in particular, an adhering step of a pair of disc substrates by using an adhesive included in production steps of DVD (digital versatile disc), a liquid resin supplying step for forming an covering layer which transmits light included in production steps of a next generation optical disc called a blu-ray disc, and a step of adhering a pair of disc substrates via a much thinner adhesive layer than an adhesive layer of the above-described DVD included in production steps of a next generation optical disc called HD-DVD (high definition-digital versatile disc).
With regard to such optical discs, it is not possible to accurately read data recorded on the optical disc if large bubbles are included in the adhesive layer or the resin layer, hence, a liquid resin supplying step has included a defoaming step for removing bubbles from the liquid resin. With regard to existing DVDs, comparatively large bubbles are acceptable, and liquid material supplying methods and apparatuses which are currently proposed can be applied to production steps of the optical discs. However, the next generation optical discs have a strict limitation for the size of such bubbles included in the adhesive layer, the resin layer, and the like. For example, existing DVDs have a limitation of 100 μm on the diameter of bubbles included in the adhesive layer and the resin layer, but the next generation optical disc requires a much smaller diameter with regard to the included bubbles. In addition, there is a possibility in which the viscosity of a liquid resin used for forming the adhesive layer or the resin layer of the next generation optical disc is severalfold higher than the DVD, and it is very difficult to defoam bubbles so as to achieve the limitation by using the existing liquid material supplying methods and apparatuses (for example, see Patent Document 1 and 2) that are used for producing DVDs, hence, it is not possible to apply these to the production of next generation optical discs.
The inventors of the present invention have conducted various experiments based on an idea in which, in order to reduce the size of bubbles included in the adhesive layer and the resin layer of the next generation optical disc, it is necessary to reduce the size of bubbles included in the liquid material before being supplied to a objective member. As a result, one main reason it was difficult to reduce the size of bubbles included in the liquid material was found, that is, in the conventional liquid material supplying apparatuses and methods, as described in Patent Document 1, in which a mechanical operation of opening/closing the liquid material is conducted at a stage which is comparatively close to a discharging step of the liquid material on the objective member. This point is explained below in detail. For example, as described in Patent Document 1, in a case in which a supplying/stopping operation of the liquid material is conducted by opening/closing a liquid path with, for example, a valve member, the valve member conducts an opening/closing operation in the liquid material, the liquid material is mechanically rolled or ruffled by the valve member, and new bubbles and large bubbles are generated by gathering small bubbles included in the liquid material. In particular, an adhesive and/or a liquid resin with a higher viscosity than existing DVDs are applied to the next generation optical discs, and it is difficult to form a film without including bubbles if the liquid material with such a high viscosity is used.
In addition, not only in a discharging system disclosed in Patent Document 2, but in all discharging systems, it was found that bubbles were easily generated at each step of the discharging system. For example, in Patent Document 2, bubbles included in the adhesive are removed in a warming tank. However, on a liquid path which supplies the adhesive from which bubbles are removed to an adhesive discharging head, there are multiple pipe members, pumps, temperature control tanks, and the like which are provided, and finally the adhesive is discharged from the adhesive discharging head. In addition, in the same manner as Patent Document 1, the adhesive discharging head mechanically discharges/stops the liquid material. However, it was found that, in the liquid material including the adhesive supplied through the liquid path, bubbles are included or generated, for example, by a seam of pipes, or a small bump or concave portion of the pipe or when the liquid material is lead inside a tank from the pipe, is lead to the pipe member out of various tanks, is lead into or out of the pump or is lead into the adhesive discharging head from the pipe. Therefore, in order to reduce bubbles included in the discharged adhesive as much as possible, it is necessary to avoid generating bubbles and to pay attention to reduce the size of bubbles at each step of the discharging system of the liquid material.
[Patent Document 1] Japanese Patent Application, First Publication No. 2004-275859
[Patent Document 2] Japanese Patent Application, First Publication No, 2001-067740